Quasi-one-dimensional ZrS₃ nanoflakes attract intense interest attributed to their superior electrical and optical anisotropy, stemming from the low symmetry in the crystal structure. However, the conventional chemical vapor transport method for synthesizing bulk ZrS₃ is limited by morphology and size controllability. It is highly desirable to propose a facile way to precisely synthesize ZrS₃ nanoflakes. In this work, the chemical vapor deposition method is proposed as a feasible way to synthesize ZrS₃ nanoflakes. The effects of various substrates and temperatures on ZrS₃ synthesis have been investigated. For the as-grown ZrS₃, good crystallinity is confirmed with X-ray diffraction and transmission electron microscopy. The structure and interlayer coupling are investigated with Raman scattering spectroscopy. The strong in-plane anisotropy and interlayer coupling of the ZrS₃ nanoflakes are illustrated with angle-resolved Raman spectroscopy and temperature-dependent Raman characterization, respectively. This study demonstrates a feasible way for the synthesis of transition metal trisulfides, which may shed new light on the research of other two-dimensional anisotropic transition metal materials.

Ag nanowire (NW) film is the promising next generation transparent conductor. However, the residual long-chain polyvinylpyrrolidone (PVP, introduced during the synthesis of Ag NWs) layer greatly deteriorates the carrier transport capability of the Ag NW film and as well its long-term stability. Here, we report a one-step I⁻ ion modification strategy to completely replace the PVP layer with an ultrathin, dense layer of I⁻ ions, which not only greatly diminishes the resistance of the Ag NW film itself and that at interface of the Ag NW film and a functional layer (e.g., a current collect electrode) but also effectively isolates the approaching of corrosive species. Consequently, this strategy can simultaneously improve the carrier transport properties of the Ag NW film and its long-term stability, making it an ideal electric component in diverse devices. For example, the transparent heater and pressure sensor made from the I⁻-wrapped Ag NW film, relative to their counterparts made from the PVP-wrapped Ag NW film, deliver much improved heating performance and pressure sensing performance, respectively. These results suggest a facile post treatment approach for thin Ag NW film with improved carrier transport properties and long-term stability, thereby greatly facilitating its downstream applications.

The accomplishment of nanowelding typically requires the input of high energy, possibly causing appreciable damages to the brittle nanomaterial. Herein, we report an external field (EF, i.e., light, direct current (DC), and alternating current (AC))-strengthened Ostwald nanowelding (ONW) strategy to enable low-temperature nanowelding of Au nanoparticles (NPs) with nanoscale spacing in solution and propose an electron localization mechanism to understand it. We reveal that the EF-derived local electrons not only greatly strengthen the dissolution of surface atoms and the reduction of Au³⁺ ions dissolved, but also confine (together with ordered water molecules) the transport of Au³⁺ ions within the nanogap. Consequently, the electrochemical Ostwald ripening (OR) process of the Au NPs is actively strengthened, which, along with the local electron-strengthened surface atom diffusion (as a result of the strong electrostatic repulsion created), enables feasible ONW for solution processing of interdigital electrodes (IDEs) from Au NPs and high-performance transparent conductor (TC) from Ag nanowires (NWs). Our low-temperature nanowelding strategy offers an efficient interconnection technique for the processing of functional nanodevices from individual nanomaterials.

Potassium-ion batteries (PIBs) are of academic and economic significance, but still limited by the lack of highly active electrode materials for de-/intercalation of large-radius K ions. Herein, an interconnected nitrogen/sulfur co-doped carbon nanosheep bundle (N/S-CSB) was proposed as the potassium ions storage material. The rich co-doping of nitrogen/sulfur of N/S-CNB with three-dimensional hierarchical bundled array structure yields distensible interlayer spaces to buffer the volume expansion during K⁺ insertion/extraction, offers more electrochemical active sites to obtain a high specific capacity, and provides efficient channels for fast ion/electron transports. Therefore, the N/S-CSB anode achieved high reversible specific capacity of 365 mAh/g obtained at 50 mA/g after 200 cycles with a coulombic efficiency (CE) close to 100%, high rate performance and long cycle stability. Moreover, the in-situ Raman spectra indicated outstanding reaction kinetics of as-prepared N/S-CSB anode.

The two-dimensional transition metal dichalcogenides (TMDs) have attracted intense interest as an atomically thin semiconductor channel for the continued transistor scaling. However, with a dangling bond free surface, it has been a key challenge to reliably integrate high-quality gate dielectrics on TMDs. In particular, the atomic layer deposition of dielectrics on TMDs typically features highly non-uniform nucleation and produces a highly rough or porous dielectric film with rich pinholes that are prone to further damage during the gate integration process. Herein we report a van der Waals (vdW) integration route towards highly reliable gate metal integration on porous dielectrics. The physical lamination process employed by the vdW integration avoids the direct deposition of metal electrodes into porous dielectrics to ensure reliable gate integration and produce low gate leakage devices. The electrical measurements demonstrate the vdW integrated MoS₂ top gate devices exhibit substantially reduced gate leakage current that is about 3–5 orders of magnitude smaller than that with deposited metal electrodes. Furthermore, we show the vdW integration process can be used to create high performance top-gated MoS₂ transistors with ultrathin Al₂O₃ dielectrics down to 1 nm, representing the ultimate dielectric scaling for TMDs transistors. This study demonstrates that vdW integration can enable highly reliable gate integration on relatively low quality dielectrics on TMDs, and opens an interesting pathway to high-performance top-gate transistors using dangling bond free two-dimensional (2D) semiconductors.

Palladium diselenide (PdSe₂), a stable layered material with pentagonal structure, has attracted extensive interest due to its excellent electrical and optoelectronic performance. Here, we report a reliable process to synthesize PdSe₂ via chemical vapor deposition (CVD) method. Through systematic regulation of temperature in the growth process, we can tune the thickness, size, nucleation density and morphology of PdSe₂ nanosheets. Field-effect transistors based on PdSe₂ nanosheets exhibit n-type behavior and present a high electron mobility of 105 cm²·V^-1·s^-1. The electrical property of the devices after 6 months keeping in the air show little change, implying outstanding air-stability of PdSe₂. In addition, PdSe₂ near-infrared photodetector shows a photoresponsivity of 660 A·W^-1 under 914 nm laser. These performances are better than those of most CVD-grown 2D materials, making ultrathin PdSe₂ a highly qualified candidate material for next-generation optoelectronic applications.

Mulitipe stoichiometric ratio of two-dimensional (2D) transition metal dichalcogenides (TMDCs) attracted considerable interest for their unique chemical and physical properties. Here we developed a chemical vapor deposition (CVD) method to controllably synthesize ultrathin NiS and NiS₂ nanoplates. By tuning the growth temperature and the amounts of the sulfur powder, 2D non-layered NiS and NiS₂ nanoplates can be selectively prepared with the thickness of 2.0 and 7.0 nm, respectively. X-ray diffraction (XRD) and transmission electron microscopy (TEM) characterization reveal that the 2D NiS and NiS₂ nanoplates are high-quality single crystals in the hexagonal and cubic phase, respectively. Electrical transport studies show that electrical conductivities of the 2D NiS and NiS₂ nanoplates are as high as 4.6 × 10⁵ and 6.3 × 10⁵ S·m^-1, respectively. The electrical results demonstrate that the synthesized metallic NiS and NiS₂ could serve as good electrodes in 2D electronics.

Heterostructures combined by different individual two-dimensional (2D) materials are essential building blocks to realize unique electronic, optoelectronic properties and multifunctional applications. To date, the direct growth of 2D/2D atomic van der Waals heterostructures (vdWHs) have been extensively investigated. However, the heterostructures from 2D inorganic molecular crystals and atomic crystals have been rarely reported. Here we report two-step direct epitaxial growth of the inorganic molecular-atomic Sb₂O₃/WS₂ vdWHs. The thickness of Sb₂O₃ nanosheets on WS₂ nanosheets can be tuned by variable growth temperatures. Oriented growth behavior of Sb₂O₃ on WS₂ was determined through statistics. Optical images, Raman spectra, Raman mappings and selected-area electron diffraction (SAED), etc., reveal that Sb₂O₃/WS₂ heterostructures are vertically stacked with high crystal quality. Electrical transport measurements demonstrate that the heterotransistors based on the heterostructures possess high current on/off ratio of 5 × 10⁵, obvious gate-tunable and current rectification output characteristics. Optoelectronic characterizations show that the heterostructures have a clear photoresponse with high responsivity of 16.4 A/W. The growth of vdWHs from 2D inorganic molecular-atomic crystals may open up new opportunities in 2D functional electronics and optoelectronics.

A prerequisite for widespread applications of atomically thin transition metal dichalcogenides in future electronics is to achieve reliable electrical contacts, which is of considerable challenge due to the difficulties in selectively doping and inevitable physical damages of these atomically thin materials during typical metal integration process. Here, we report the in situ growth of ultrathin metallic NiSe single crystals on WSe₂ in which the metallic NiSe nanosheets function as the contact electrodes to WSe₂, creating an interface that is essentially free from chemical disorder. The NiSe/WSe₂ heterostructures also exhibit well-aligned lattice orientation between the two layers, forming a periodic Moiré pattern. Electrical transport studies demonstrate that the NiSe nanosheets exhibit an excellent metallic feature, as evidenced by the extra-high electrical conductivity of up to 1.6×10⁶ S·m^-1. The WSe₂ transistors with the NiSe contact show field-effect mobilities (μ_FE) more than double that with Cr/Au electrodes. This study demonstrates an effective pathway to achieve reliable electrical contacts to the atomically thin 2D materials, and maybe readily extended for fabricating 2D/2D low-resistance contacts for a variety of transition metal dichalcogenides.

The mixed-dimensional integration of two-dimensional (2D) materials with non-2D materials can give rise to prominent advances in performance or function. To date, the mixed-dimensional one-dimensional (1D)/2D heterostructures have been fabricated using various physical assembly approaches. However, direct epitaxial growth method which has notable advantages in preparing large-scale products and obtaining perfect interfaces is rarely investigated. Herein, we demonstrate for the first time the direct synthesis of the 1D/2D mixed-dimensional heterostructures by sequential vapor-phase growth of Sb₂Se₃ nanowires on WS₂ monolayers. X-ray diffraction (XRD) pattern and Raman spectrum confirm the composition of the Sb₂Se₃/WS₂ heterostructures. Transmission electron microscope (TEM) measurement demonstrates high quality of the heterostructures. Electrical transport characterization reveals that Sb₂Se₃ nanowire exhibits p-type characteristic and that WS₂ monolayer exhibits n-type behavior, and that the p-n diode from 1D/2D mixed-dimensional Sb₂Se₃/WS₂ heterostructure possesses obvious current rectification behavior. Optoelectronic measurements of the heterostructures show apparent photovoltaic response with an open-circuit voltage of 0.19 V, photoresponsivity of 1.51 A/W (V_ds = 5 V) and fast response time of less than 8 ms. The van der Waals epitaxial growth mode of Sb₂Se₃ nanowires on WS₂ monolayers is verified by stripping the Sb₂Se₃ nanowire from the heterostructures using tape. Together, the direct van der Waals epitaxy opens a facile pathway to 1D/2D mixed-dimensional heterostructures for functional electronic and optoelectronic devices.